Sunday, December 23, 2012

Utilizing the DNA of a Close Cousin, Part Two

The arrival of my mother's maternal first cousin at 23andMe enables me to more definitely categorize our genetic cousins into branches of the tree using autosomal DNA.

Of particular concern was the beginning of chromosome 15.  My mother has several matches that share a long segment with her from the beginning, zero, through 24,000,000.  These genetic cousins are usually from Latvia or at least one parent was.  I figured that these people were from my mother's father's side of the family, as my maternal grandmother has no Latvian ancestry known to me.  But we have to keep an open mind about our notions of our origins when we analyze our DNA.

Jody's mom versus JZ, TD, and dg.
Question posed by this match:  Do these cousins match through the paternal or maternal side?

When my mother's brother tested, he did not match any of these people.  In addition, he and my mother did not match on chromosome 15 until the 24,000,000 mark.  This is because you have two sides to your chromosomes:  one is from mom, the other from dad.  My mother and uncle did not inherit the same piece of the beginning of chromosome 15 from their mother.

So I could not be sure if these people matched my mother through her father or her mother.

Then along came the maternal first cousin, F.O.  He and my mother match at the beginning of chromosome 15, thus revealing my mother's maternal side of this segment. 

Isn't it amazing that in all of these people, the chromosome "broke" in the same spot?

Comparing F.O. to the other people who match my mother at the beginning of chromosome 15, we find that F.O. does not match these people.  So we can conclude that this group of Latvian cousins matches my mother through her father and not her mother.  Now to find the elusive common ancestor of all of them . . .

Maternal first cousin F.O. versus the Latvian matches.

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